Tractor bulldozer



Nov. 19, 1940. T. R. PAULsEN 2,221,813

TRACTOR BULLDOZER Filed Dec. 17, 1937,. 2 Sheets-Sheet l F15 y vmaaf/fae@ INV ENTOR.

BY WWWZW ATTORNEY.

Nov. 19, 1940.

T. R. PAULSEN TRACTOR BULLDOZER Filed Dec. lT, 1937 2' sheets-sheet 2 k L ealfse/m, F' j INVBNTOR. 42 Ji/Y ATTORNEY.

Patented Nov. 19, 1940\ UNITED STATES PATENT OFFICE TRACTOR BULLDOZER Application December 17, 1937, Serial No. 180,292

2 Claims.

My invention relates to new and useful improvements in bulldozers, and more particularly to that type of bulldozer in which the scraping blade is pushed ahead of a tractor.

Such devices are usually designed for attachment to some conventional type of tractor.- They consist of a blade, two arms pivoted on the tractor for pushing the blade, and means to raise and lower either arm with a certain degree of independence from the lowering and raising of the other arm. The last-mentioned means usually consists of one or two hydraulic cylindersactuated by a pump driven by the engine of the tractor.

If two such cylinders are used, it is convenient to have them controlled by a single control-valve, but this interferes with the flexibility of the moving parts.

Accordingly it is the principal object of my invention to provide means whereby the average position of the two pistons is controlled by the valve, while leaving the pistons free to reciprocate compensatingly in all positions; and whereby whenever4 thetwo pistons are both shifted either to extreme out or extreme in position, both pistons will speedily assume an average position just short of their former extreme position, and thus become free to reciprocate compensatingly as already stated.

In addition to my principal object, above stated, I have Worked out a number of novel and useful details, which will be readily evident as the description progresses.

My invention consists in the novel parts and r in the combination and arrangement thereof,

which are defined in the appended claims, and of which one embodiment is exemplified in the accompanying drawings, which are hereinafter particularly described and explained.

Throughout the description, the same reference number is applied to the same member or to simi- .lar members.

Figure 1 is a plan view of a tractor and bullr dozer embodying my invention.

Figure 2 is a side elevation of this same tractor and bulldozer.

Figure 3 is a longitudinal section of one of my cylinders.

Figures 4 and 5 are comparativegures, somewhat conventionalized, to illustrate the function performed by a certain fluid by-pass, which forms one of the elements oi my invention.

Referring now to Figures l and 2, We see that I I is a conventional tractor, mounted on creeping traction I2. These creeping traction elements are (Cl. Gil-52) pivoted on propelling shaft I3, and their front ends have considerable freedom to rise and fall to conform-to unevenness of the ground.

Pivoted to each traction element I2 at I4 is a forwardly projecting arm I5. These arms support and impel a scraper blade I6.

On each side of the tractor there is a link I1 pivoted to the rear of the tractor at I8, and a link I9 pivoted to the creeping traction at 20. These two links are pivoted together at 2|, and at this point is also pivoted the elbow of a bell-crank 22.

The front end of each bell-crank supports one side of the blade I6 through a link 23.

There are two cylinders 24, each pivoted at 25 on one of the links I'I. The piston rod 26 of each cylinder is pivoted at 21 to the short arm of the bell-crank 22.

yThe rear ends of the two cylinders are connected by a pipe 28, from which a pipe 29 leads to a control-valve 30. The front ends of the two cylinders are similarly connected by a pipe 3|, from which a pipe 32 leads to the control-valve already mentioned. Thus free intercommunication between the two cylinders is maintained, regardless of the valve-setting. 'I'his is what I mean in the claims by "freely connecting together.

The control-valve may be of any conventional design, the details of which are not shown as they form no part of my invention. But the valve `should have four positions, namely: (1) to pump from the rear of the cylinders into the front, and thus retract the pistons; (2) to pump from the front of the cylinders into the rear, and thus -thrust the pistons out; (3) to close both pipe 23 and pipe 32, and thus hold the pistons; and (4) to open pipe 29 to pipe 32, and thus permit free floating of the pistons.

From the valve a pressure pipe 33 and a suction pipe 34 lead to a pump 35, actuated in any conventional manner by the main engine of the tractor. From a fluid tank 36, there runs to suction pipe 34, a pipe 31 with a check valve 38, for the purpose of keeping the system always illled with iiuid. From the suction pipe 34 to the tank 36, there runs a pipe 44 with a pressure relief valve 45, to permit compensation for the space occupied by the piston rods 26 within the cylinders 24 when the pistons are being retracted, and yet hold them against unintended retracting. r

The connection of blade I6 to arms I5 is almost rigid, for the purpose of holding the blade at all times in virtual parallelism with axle I3; points Il being sufficiently close to the axle I3 vfor this purpose. But the relative rise and fall 55 of points 2|. as the two traction elements encounter uneven groun`d, would tend to raise the two links 23 an unequal amount, inconsistent with the quasi-rigidity of the quadrilateral formed by the blade ii, the arms I5, and the axle il. Accordingly we must either sacrifice this desirable quasi-rigidity, or devise some means to compensate for the relative rise and fall of points 2l. I have chosen the latter alternative.

Accordingly (see Figure 4) I have freely interconnected the front end of my two cylinders by pipe 3i, and have freely connected the rear end of my two cylinders by pipe 20.

In Figures 4 and 5, cross-bar 39 does not represent any actual part of my apparatus. It is merely diagrammatic, to illustrate the compensating reciprocation of my two pistons which my invention permits.

Let us assume that my two pistons I0 are in the mid position illustrated in Figure 4, and that some condition encountered by cross-bar I9 tends to tilt it into the dotted-line position. 'I'he shift of the pistons to their dotted-line positions, to permit this, s in turn permitted by the free ilow of 4fluid from the rear of the upper cylinder through pipe 2l to the rear of the lower cylinder,

and the free flow of fluid from the front of the lower cylinder through pipe ll to the front of the upper cylinder. But note that the mid point of cross-bar I9 is still firmly held.

-Now assume that the pistons are at their extreme rearward position, as shown in Figure 5, .and some condition tends to tilt the cross-bar 39. This would not` be possible, were it not for the further and most important feature of my Invention.

Neither piston can move further to the rear, but either one of them can move to the front, as follows. Let us assume that the tendency 40is for the lower piston to move forwards. The

fluid to the front of it passes'through pipe 3| into the front of the upper cylinder, thus forcing fluid through the by-Dass Il around the piston 4I of that cylinder; thence through pipe 28 into the rear of the lower cylinder, thus permitting the piston of that cylinder and hence the crossbar II to assume their dotted-line positions.

It might be'thought that this situation would leave'the lower piston of Figure 5 free to move back and forth the whole length of the cylinder.

It would, were it not for the quasi-rigidity of the U formed by the arms I5 and blade il. 'I'his quasi-rigidity has already been referred to. Due

to this quasi-rigidity, a slight rising of the right tread will pull out the lower piston only a slight part of its potential travel, say to the dotted position shown in Figure 5. When the treads return to parallelism, and lthe piston tends to return to its full-line position, the device will work as in Figure 4, and the two pistons will assume an average position half way between the full-line and dotted positions in the lower cylinder of Figure 5. 'I'he cylinders areso proportioned and placed that this nearly all-in position raises the blade as high as is necessary.

Similarly if the tilting tendency were the Opposite.

By-pass 42 similarly permits tilting when the pistons are in their extreme forward positions.

It is to be noted, more'particularly from Figure 3, that each of the by-passes is closed by a checkvalve 43, so as to prevent ow in the wrong direction; flow in the wrong direction would permit the sudden bumping of the pistons against the cylinder-heads, upon arriving at extreme position. It is also to be noted that each by-pass is just barely long enough to route the fluid around the piston when the piston is in extreme position; more than this would render the device unnecessarily unstable.

Having now described and illustrated one form of my invention, I wish it to be understood that my invention is not to be limited to the specific form or arrangement of parts hereinbefore described, except insofar as-such limitations are specified in the appended claims.

I claim:

l. In combination: two fluid pressure cylinders; pistons therein; piston rods for the pistons; a fluid pressure pump, to supply fluid to the cylinders; control means interposed between the pump and the cylinders to control flow of fluid to and from the two cylinders jointly; a pipe freely connecting together the front ends of the two cylinders when the control means is set to disconnect the pump from the cylinders; a pipe freely connecting together the rear ends of the two cylinders when the control means is set to disconnect the pump from the cylinders; at each end of each cylinder a by-pass to pass iluid around the piston when in extreme position at that end oi" the cylinder; a check-valve in such bypass, so as to permit flow only toward the adjacent end of the cylinder; and an actuated element connected to the outer ends of the two piston rods for limited movement relative to the piston rods; whereby limited compensating relative movement of the pistons is rendered possible at either end of their stroke.

2 In combination: two uid pressure cylinders; pistons therein, piston rods for the pistons: a fluid pressure pump, to supply iluid to the cylinders; control means interposed between the pump and the cylinders to control flow of fluid to and from the cylinders, so as selectively to thrust, retract, and hold the two pistons jointly; a pipe freely connecting together the front ends of the two cylinders when the control means is set to hold; a pipe freely connecting together the rear ends of the two cylinders when the control means is set to hold; at one end of one cylinder and at the corresponding end of the other cylinder, a

by-pass to pass iluid around the piston when in V extreme position; a check-valve in such by-pass, so as to permit flow only toward the adjacent end of the cylinder; and an actuated element connected to the outer ends of the two pistonrods for limited movement relative to the piston rods; whereby limited compensating relative movement of the pistons is rendered possible at one end of their stroke.

THOMAS R. PAULSEN. 

